DOCSLIB.ORG

EROSION of the UNITED STATES SHORELINE a Variety of Reference

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
EROSION of the UNITED STATES SHORELINE a Variety of Reference EROSION OF THE UNITED STATES SHORELINE ORRIN H. PILKEY, JR AND E. ROBERT THIELER Duke Universic. Depunmenf of Geology. Old Chemist? Building. Durham. North Crtrolina 177015 ABSTRACT: Over 75 percent of the United States ocean shoreline is eroding (retreating landward). Shoreline progradation. where oc- curring, is generally assumed to be a temporary phenomenon. When affecting a developed area, shoreline retreat is usually termed erosion. but considerable confusion remains over the use of this term. Retreat and progradation refer to a change in shoreline position. whereas erosion and accretion refer to volumetric changes in the subaerial beach. As used in this paper. however. erosion refers to any form of shoreline retreat. consistent with common usage. Coastal erosion is a fundamental and widespread process on U.S. and world shorelines. Evidence. particularly on banier-island coasts. indicates that in the past few decades or millenia. erosion may have become a more widespread process. Possible causes of this change include the effect of humans, shoreface steepening. or an increase in the rate of eustatic sea-level rise. Mechanisms responsible for shoreline erosion arc highly variable. both temporally and geographically. In addition, our understanding of shoreline sediment-transport dynamics is incomplete. Consequently, we are presently unable to predict accurately future shoreline- retreat rates related to continued sea-level rise. The Bmun Rule. for example. predicts little shoreline retreat relative to using, as a pdictive tool, the slope of the land surface over which sea level is expected to rise. WHAT IS COASTAL EROSION? a variety of reference features. measurement techniques, and Defining erosion in the coastal environment is difficult. rate-of-ihange calculations. Thus, whereas CEIS represents Various terms are used to describe the process, including the best available data for the U.S. as a whole, much work drowning, coastal erosion, shoreline erosion, beach ero- is needed to document regional and local erosion rates ac- sion. shoreline retreat, beach retreat, and shoreline reces- curately. sion. Strictly speaking, retreat and progradation refer to a When examined in detail, such as on a state-by-state ba- change in shoreline position; erosion and accretion refer to sis, the actual percentage of eroding shoreline is generally volumetric changes in the subaerial beach (Wood and oth- much higher than the coastwide averages shown in Figure ers, 1988; Oertel and others, 1989). The term beach ero- 1 suggest. This discrepancy is likely due to the large amount sion, however, is deeply ingrained in the public lexicon to of shoreline for which "no data" exist and the coarse res- refer to any form of shoreline retreat (usually the change olution of CEIS. Dolan and others (1990b). for example, in position of the high-tide line); we shall here use it in the report that 78 percent of the Delaware shoreline is eroding; same broad sense as does the general public. Maryland, 94 percent; Virginia, 72 percent; and North Car- When dealing with shorelines and beaches, it is crucial olina, 72 percent. Griggs (1987a) states that approximately to distinksh between erosion and an erosion ~roblem.Many 86 percent of the California shoreline is eroding. kilometgrs of undeveloped U.S. shoreline & eroding (re- treating landward) and, as a rule, such locations are not WHY UBIQUITOUS EROSION? considered to be societal problems. Erosion and retreat of the shoreline are, in fact, critically important processes in Coastal erosion is a fundamental and widespread process the evolution of Holocene coastal landforms. Estuaries, la- not only on U.S. but also world shorelines. There is some goons, spits, banier islands, sea cliffs, and many other coastal evidence, however, that such has not always been the case. landforms all owe their shape and depositional patterns to Examination of the U.S. barrier-island shoreline, for ex- erosion, at least in part. It is only when humans interfere ample, indicates that fundamental changes in depositional with or get in the way of shoreline erosion that it is rec- patterns have recently taken place. Many barrier islands are ognized as a problem. A broad discussion of the U.S. coastal- regressive, indicating that a seaward accretion or widening erosion problem, along with methodology, political impli- of the island occurred over the last 2 to 4 ka. Within the cations, and costs for mitigation is furnished by the Na- last several hundred years, however, a profound change has tional Research Council (1990). taken place and shoreline retreat has replaced shoreline pro- gradation. In other words, barrier islands are becoming in- U.S. SHORELINE-EROSION RATES creasingly transgressive. Most regressive banier islands (e.g., Erosion rates for the contiguous U.S. shoreline, based Bogue Banks, North Carolina, and Galveston Island, Texas) on data in the Coastal Erosion Information System (CEIS; are now eroding on both the ocean and lagoon sides. May and others, 1982), have been compiled by May and Possible explanations for increased worldwide erosion others (1983) and Dolan and others (1985; Tables 1 and 2; include the effects of humans-shoreline stabilization and Fig. 1). CEIS includes shoreline-change data for the At- river damming; sand supply reduction-shoreface steep- lantic, Gulf of Mexico, Pacific and Great Lakes coasts, as ening; and a recent increase in the rate of eustatic sea-level well as for major bays and estuaries. The data in CEIS are rise. However appealing, each of these possibilities leaves drawn from a variety of sources, including published re- certain questions unanswered. For example, humans cer- ports, historical shoreline-change maps, field surveys, and tainly contribute to coastal erosion in some locations, but aerial-photograph analyses. However, the lack of a stan- completely undeveloped areas such as the bamer-island dard method among coastal scientists for analyzing shore- system on the Pacific coast of Colombia are also eroding line changes has resulted in the inclusion of data utilizing at high rates. Quaternary Coasts of the United States: Muine and Lacusvine Systems. SEPM Special Publication No. 48 Copyright 0 1992. SEPM (Society for Sedimcnfaiy Geology). ISBN 0-918985-98-6 ORRIN H. PILKEY. JR AND E. ROBERT THIELER TABLEI .-SHORELINE RATES OF CHANGE FOR REGIONS AND STATES Mean SUndmd Region trn/y~l Deviation ~mgel Atlantic Coast -0.8 3.2 25.5/-24.6 Maine -0.4 0.6 1.91-0.5 New Hampshire -0.5 - -0.5/-0.5 Massachu~ns -0.9 1.9 4.5/-4.5 19 Rho& Islad -0.5 0. I -0.3/-0.7 I Aa New York 0.1 3.2 18.8/-2.2 a- m New Jersey zs.S/- 15.0 Delaware 5.0/-2.3 Atlantic Coast Gulf of Mexico Maryland 1.3/-8.8 Virginia 0.9/-24.6 Nmh Carolina 9.4/-6.0 South Carolina 5.9/-17.7 Erosion Rate (m/lvr) Georgia 5.0/-4.0 Florida 5.0/-2.9 Gulf of Mexico 8.8/- 15.3 Florida 8.8/-4.5 1 1.1-2 Alabama 0.8/-3.1 Mississippi 0.6/-6.4 Louisiana 3.4/- 15.3 Texas 0.8/-5.0 Pacific Coast 10.0/-4.2 El NoDw California 10.0/-4.2 Oregon -0.1 1.4 SO/-5.0 FIG. 1.-Pie charts of erosion rates on the U.S. open-ocean coastline. -0.5 2.2 Washington 5'0/-3'9 The large amount of shoreline classified as "no data" likely results in 'Positive values indicate accretion; negative values indicate erosion. (After Dolan an artificially low figure for the total percentage of eroding shoreline (see and others. 1985.) text for discussion). (After Dolan and others, 1990a). TABU 2.-SHORELINE RATES OF CHANGE FOR COASTAL On barrier-island coasts, erosion rates must be examined LANDFORM nPEs in the context of the total barrier-island system. The con- current development of transgressive and regressive bar- -- riers along the Texas coast, for example, is related to the Burier islands longshore distribution of sediment sources and sinks (Mor- Atlantic Coast -0.8 3.4 25.5/-24.6 Maine-New Yorlr -0.3 2.6 4.51-1.5 ton, 1979; Numrnedal, 1983). New York-North Carolina -1.5 4.5 25.5/-24.6 Shoreline erosion on the Texas coast predominates at del- Nonh Carolina-Florida -0.4 2.6 9.4/- 17.7 taic headlands, such as the Rio Grande and Brazos deltas. Gulf of Mexico -0.6 1.5 8.8/-4.3 Florida-Louisana -0.5 1.7 8.8/-4.3 In the central portion of each embayment between the del- Louisiana-Texas -0.8 1.2 0.8/-3.5 taic headlands, accretion or at least relatively slow erosion Sud beaches Atlantic Coast -1.0 I .O 2.0/-4.5 occurs (Morton, 1979). The eroding deltaic headlands are Maine-Massachusetts -0.7 0.5 -0.5/-2.5 the source of sand for the accreting shoreline between river Massachusetts-New Jersey -1.3 1.3 2.0/-4.5 mouths. Gulf of Mexico -0.4 1.6 8.8/-4.5 Pacifif Coast -0.3 1.O 0.7/-4.2 Evolution of the Louisiana coast is similarly affected by Sad beaches with rock headland -0.3 1.9 lO.O/-5.0 regional-scale processes. Penland and others (1985) dem- Pocket beaches onstrated a cyclic relation between Mississippi Delta lobe- Atlantic Coa5t -0.5 - -0.5/-0.5 Prifu Coast -0.2 1.1 5.01- I. I switching events and barrier development and destruction. Dcltsr -2.5 3.5 8.8/- 15.3 Extremely rapid shoreline-erosion rates prevail no matter Mud flur Gulf of Mexico -1.9 2.2 3.4/-8.1 what the stage of barrier development in this cycle.
Load more

Recommended publications
  • Coastal Erosion - Orrin H
    COASTAL ZONES AND ESTUARIES – Coastal Erosion - Orrin H. Pilkey, William J. Neal, David M. Bush COASTAL EROSION Orrin H. Pilkey Program for the Study of Developed Shorelines, Division of Earth and Ocean Sciences, Duke University, Durham, NC, U.S.A. William J. Neal Department of Geology, Grand Valley State University, Allendale, MI, USA. David M. Bush Department of Geosciences, State University of West Georgia, Carrollton, GA, USA. Keywords: erosion, shoreline retreat, sea level rise, barrier islands, beach, coastal management, shoreline armoring, seawalls, sand supply Contents 1. Introduction 2. Causes of Erosion 2.1. Sea Level Rise 2.2. Sand Supply 2.3. Shoreline Engineering 2.4. Wave Energy and Storm Frequency 3. "Special" Cases 4. Solutions to Coastal Erosion 5. The Future Glossary Bibliography Biographical Sketches Summary Almost all of the world’s shorelines are retreating in a landward direction—a process called shoreline erosion. Sea level rise and the reduction of sand supply to the shoreline by damming of rivers, armoring of shorelines and the dredging of navigation channels are among the major causes of shoreline retreat. As sea levels continue to rise, sometimesUNESCO enhanced by subsidence caused – byEOLSS oil and water extraction, global erosion rates should increase in coming decades. Three response alternatives are available to "solve" the erosionSAMPLE problem. These are cons tructionCHAPTERS of seawalls and other engineering structures, beach nourishment and relocation or abandonment of buildings. No matter what path is chosen, response to the erosion problem is costly. 1. Introduction Coastal erosion is a major problem for developed shorelines everywhere in the world. Such erosion is regarded as a coastal hazard and is a common focus of local and national coastal management.
    [Show full text]
  • Coastal Flood Defences - Groynes
    Coastal Flood Defences - Groynes Coastal flood defences are key to protecting our coasts against flooding, which is when normally dry, low lying flat land is inundated by sea water. Hard engineering methods are forms of coastal flood defences which mitigate the risk of flooding and coastal erosion and the consequential effects. Hard Engineering Hard engineering methods are often used as a temporary measure to protect against coastal flooding as they are costly and only last for a relatively short amount of time before they require maintenance. However, they are very effective at protecting the coastline in the short-term as they are immediately effective as opposed to some longer term soft engineering methods. But they are often intrusive and can cause issues elsewhere at other areas along the coastline. Groynes are low lying wood or concrete structures which are situated out to sea from the shore. They are designed to trap sediment, dissipate wave energy and restrict the transfer of sediment away from the beach through long shore drift. Longshore drift is caused when prevailing winds blow waves across the shore at an angle which carries sediment along the beach.Groynes prevent this process and therefore, slow the process of erosion at the shore. They can also be permeable or impermeable, permeable groynes allow some sediment to pass through and some longshore drift to take place. However, impermeable groynes are solid and prevent the transfer of any sediment. Advantages and Disadvantages +Groynes are easy to construct. +They have long term durability and are low maintenance. +They reduce the need for the beach to be maintained through beach nourishment and the recycling of sand.
    [Show full text]
  • Coastal Processes and Causes of Shoreline Erosion and Accretion Causes of Shoreline Erosion and Accretion
    Coastal Processes and Causes of Shoreline Erosion and Accretion and Accretion Erosion Causes of Shoreline Heather Weitzner, Great Lakes Coastal Processes and Hazards Specialist Photo by Brittney Rogers, New York Sea Grant York Photo by Brittney Rogers, New New York Sea Grant Waves breaking on the eastern Lake Ontario shore. Wayne County Cooperative Extension A shoreline is a dynamic environment that evolves under the effects of both natural 1581 Route 88 North and human influences. Many areas along New York’s shorelines are naturally subject Newark, NY 14513-9739 315.331.8415 to erosion. Although human actions can impact the erosion process, natural coastal processes, such as wind, waves or ice movement are constantly eroding and/or building www.nyseagrant.org up the shoreline. This constant change may seem alarming, but erosion and accretion (build up of sediment) are natural phenomena experienced by the shoreline in a sort of give and take relationship. This relationship is of particular interest due to its impact on human uses and development of the shore. This fact sheet aims to introduce these processes and causes of erosion and accretion that affect New York’s shorelines. Waves New York’s Sea Grant Extension Program Wind-driven waves are a primary source of coastal erosion along the Great provides Equal Program and Lakes shorelines. Factors affecting wave height, period and length include: Equal Employment Opportunities in 1. Fetch: the distance the wind blows over open water association with Cornell Cooperative 2. Length of time the wind blows Extension, U.S. Department 3. Speed of the wind of Agriculture and 4.
    [Show full text]
  • Management of Coastal Erosion by Creating Large-Scale and Small-Scale Sediment Cells
    COASTAL EROSION CONTROL BASED ON THE CONCEPT OF SEDIMENT CELLS by L. C. van Rijn, www.leovanrijn-sediment.com, March 2013 1. Introduction Nearly all coastal states have to deal with the problem of coastal erosion. Coastal erosion and accretion has always existed and these processes have contributed to the shaping of the present coastlines. However, coastal erosion now is largely intensified due to human activities. Presently, the total coastal area (including houses and buildings) lost in Europe due to marine erosion is estimated to be about 15 km2 per year. The annual cost of mitigation measures is estimated to be about 3 billion euros per year (EUROSION Study, European Commission, 2004), which is not acceptable. Although engineering projects are aimed at solving the erosion problems, it has long been known that these projects can also contribute to creating problems at other nearby locations (side effects). Dramatic examples of side effects are presented by Douglas et al. (The amount of sand removed from America’s beaches by engineering works, Coastal Sediments, 2003), who state that about 1 billion m3 (109 m3) of sand are removed from the beaches of America by engineering works during the past century. The EUROSION study (2004) recommends to deal with coastal erosion by restoring the overall sediment balance on the scale of coastal cells, which are defined as coastal compartments containing the complete cycle of erosion, deposition, sediment sources and sinks and the transport paths involved. Each cell should have sufficient sediment reservoirs (sources of sediment) in the form of buffer zones between the land and the sea and sediment stocks in the nearshore and offshore coastal zones to compensate by natural or artificial processes (nourishment) for sea level rise effects and human-induced erosional effects leading to an overall favourable sediment status.
    [Show full text]
  • Coastal Zone and Estuaries
    CONTENTS COASTAL ZONE AND ESTUARIES Coastal Zone and Estuaries - Volume 1 No. of Pages: 540 ISBN: 978-1-84826-016-0 (eBook) ISBN: 978-1-84826-466-3 (Print Volume) For more information of e-book and Print Volume(s) order, please click here Or contact : [email protected] ©Encyclopedia of Life Support Systems (EOLSS) COASTAL ZONES AND ESTUARIES CONTENTS Coastal Zone and Estuaries 1 Federico Ignacio Isla, Centro de Geología de Costas y del Cuaternario, Universidad Nacional de Mar del Plata, Argentina 1. The Coastal Zone 1.1. Climate Change 1.2. Sea Level and Sea Ice Fluctuations 1.3. Coastal Processes 1.4. Sediment Delivery 1.5. Beaches 1.6. Tidal Flats and Marshes 1.7. Mangroves 1.8. Coral Reefs, Coral Cays, Sea Grasses, and Seaweeds 1.9. Eutrophication and Pollution 1.10. Coastal Evolution 2. Estuarine Environments 2.1. Estuaries 2.2. Coastal Lagoons 2.3. Deltas 2.4. Estuarine Evolution 3. Coastal Management 4. New Techniques in Coastal Science 5. Concluding Remarks Coastal Erosion 32 Orrin H. Pilkey, Program for the Study of Developed Shorelines, Division of Earth and Ocean Sciences, Duke University, Durham, NC, U.S.A. William J. Neal, Department of Geology, Grand Valley State University, Allendale, MI, USA. David M. Bush, Department of Geosciences, State University of West Georgia, Carrollton, GA, USA. 1. Introduction 2. Causes of Erosion 2.1. Sea Level Rise 2.2. Sand Supply 2.3. Shoreline Engineering 2.4. Wave Energy and Storm Frequency 3. Special Cases 4. Solutions to Coastal Erosion 5. The Future Waves and Sediment Transport in the Nearshore Zone 43 Robin G.
    [Show full text]
  • Types and Causes of Beach Erosion Anomaly Areas in the U.S. East Coast Barrier Island System: Stabilized Tidal Inlets
    Middle States Geographer, 2007, 40:158-170 TYPES AND CAUSES OF BEACH EROSION ANOMALY AREAS IN THE U.S. EAST COAST BARRIER ISLAND SYSTEM: STABILIZED TIDAL INLETS Francis A. Galgano Jr. Department of Geography and the Environment Villanova University 800 Lancaster Avenue Villanova, Pennsylvania 19085 ABSTRACT: Contemporary research suggests that most U.S. beaches are eroding, and this has become an important political and economic issue because beachfront development is increasingly at risk. In fact, the Heinz Center and Federal Emergency Management Agency (FEMA) estimate that over the next 60 years, beach erosion may claim one out of four homes within 150 meters of the U.S. shoreline. This is significant because approximately 350,000 structures are located with 150 meters of the shoreline in the lower 48 states, not including densely populated coastal cities such as New York and Miami. Along the East Coast, most beaches are eroding at 1 to 1.5 meters per year. However, beach erosion is especially problematic along so-called beach erosion anomaly areas (EAAs) where erosion rates can be as much as five times the rate along adjacent beaches. Identifying and understanding these places is important because property values along U.S. East Coast barrier islands are estimated to be in the trillions of dollars, and the resultant beach erosion may also destroy irreplaceable habitat. There are a number of factors⎯natural and anthropogenic⎯that cause beaches to erode at anomalous rates. This paper will focus on the barrier island system of the U.S. East Coast, classify beach EAAs, and examine beach erosion down drift from stabilized tidal inlets because they are perhaps the most spatially extensive and destructive EAAs.
    [Show full text]
  • 1 the Influence of Groyne Fields and Other Hard Defences on the Shoreline Configuration
    1 The Influence of Groyne Fields and Other Hard Defences on the Shoreline Configuration 2 of Soft Cliff Coastlines 3 4 Sally Brown1*, Max Barton1, Robert J Nicholls1 5 6 1. Faculty of Engineering and the Environment, University of Southampton, 7 University Road, Highfield, Southampton, UK. S017 1BJ. 8 9 * Sally Brown ([email protected], Telephone: +44(0)2380 594796). 10 11 Abstract: Building defences, such as groynes, on eroding soft cliff coastlines alters the 12 sediment budget, changing the shoreline configuration adjacent to defences. On the 13 down-drift side, the coastline is set-back. This is often believed to be caused by increased 14 erosion via the ‘terminal groyne effect’, resulting in rapid land loss. This paper examines 15 whether the terminal groyne effect always occurs down-drift post defence construction 16 (i.e. whether or not the retreat rate increases down-drift) through case study analysis. 17 18 Nine cases were analysed at Holderness and Christchurch Bay, England. Seven out of 19 nine sites experienced an increase in down-drift retreat rates. For the two remaining sites, 20 retreat rates remained constant after construction, probably as a sediment deficit already 21 existed prior to construction or as sediment movement was restricted further down-drift. 22 For these two sites, a set-back still evolved, leading to the erroneous perception that a 23 terminal groyne effect had developed. Additionally, seven of the nine sites developed a 24 set back up-drift of the initial groyne, leading to the defended sections of coast acting as 1 25 a hard headland, inhabiting long-shore drift.
    [Show full text]
  • Coastal Processes on Long Island
    Shoreline Management on Long Island Coastal Processes on Long Island Coastal Processes Management for ADAPT TO CHANGE Resilient Shorelines MAINTAIN FUNCTION The most appropriate shoreline management RESILIENT option for your shoreline is determined by a SHORELINES WITHSTAND STRESSES number of factors, such as necessity, upland land use, shoreline site conditions, adjacent conditions, ability to be permitted, and others. RECOVER EASILY Costs can be a major consideration for property owners as well. While the cost of some options Artwork by Loriann Cody is mostly for the initial construction, others will require short- or long-term maintenance costs; Proposed construction within the coastal areas therefore, it is important to consider annual and of Long Island requires the property owner to long-term costs when choosing a shoreline apply for permits from local, state and federal management method. agencies. This process may take some time In addition to any associated financial costs, and it is recommended that the applicant there are also considerations of the impacts on contacts the necessary agencies as early as the natural environment and coastal processes. possible. Property owners can also request Some options maintain and/or improve natural pre-application meetings with regulators to coastal processes and features, while others discuss the proposed project. Depending on may negatively impact the natural environment. the complexity of the site or project, property Resilient shorelines tend to work with nature owners can contact a local expert or consultant rather than against it, and are more adaptable that can assist them with understanding and over time to changing conditions. Options that choosing the best option to help stabilize their provide benefits to habitat or coastal processes shorelines and reduce upland risk.
    [Show full text]
  • Deciphering the Origin of Cyclical Gravel Front and Shoreline Progradation and Retrogradation in the Stratigraphic Record
    Deciphering the origin of cyclical gravel front and shoreline progradation and retrogradation in the stratigraphic record John J. Armitage1, Peter A. Burgess2, Gary J. Hampson3, and Philip A. Allen3 1Department of Earth Science, Royal Holloway, University of London, Egham, UK; Now at Institut de Physique du Globe de Paris, 1 rue Jussieu, Paris, 75005, France; e-mail: [email protected] 2Department of Earth Science, Royal Holloway, University of London, Egham, UK 3Department of Earth Science and Engineering, Imperial College London, London, UK May 4, 2016 1 1 Abstract 2 Nearly all successions of near-shore strata exhibit cyclical movements of the shoreline, which 3 have commonly been attributed to cyclical oscillations in relative sea level (combining eustasy 4 and subsidence) or, more rarely, to cyclical variations in sediment supply. It has become accepted 5 that cyclical change in sediment delivery from source catchments may lead to cyclical movement 6 of boundaries such as the gravel front, particularly in the proximal segments of sediment routing 7 systems. In order to quantitatively assess how variations in sediment transport as a consequence 8 of change in relative sea-level and surface run-off control stratigraphic architecture, we develop a 9 simple numerical model of sediment transport and explore the sensitivity of moving boundaries 10 within the sediment routing system to change in upstream (sediment flux, precipitation rate) and 11 downstream (sea level) controls. We find that downstream controls impact the shoreline and sand 12 front, while the upstream controls can impact the whole system depending on the amplitude of 13 change in sediment flux and precipitation rate.
    [Show full text]
  • Coastal Erosion
    Guidance for Flood Risk Analysis and Mapping Coastal Erosion February 2018 Requirements for the Federal Emergency Management Agency (FEMA) Risk Mapping, Assessment, and Planning (Risk MAP) Program are specified separately by statute, regulation, or FEMA policy (primarily the Standards for Flood Risk Analysis and Mapping). This document provides guidance to support the requirements and recommends approaches for effective and efficient implementation. Alternate approaches that comply with all requirements are acceptable. For more information, please visit the FEMA Guidelines and Standards for Flood Risk Analysis and Mapping webpage (www.fema.gov/guidelines-and-standards-flood-risk-analysis-and- mapping). Copies of the Standards for Flood Risk Analysis and Mapping policy, related guidance, technical references, and other information about the guidelines and standards development process are all available here. You can also search directly by document title at www.fema.gov/library. Coastal Erosion February 2018 Guidance Document 40 Page i Document History Affected Section or Date Description Subsection Sections 2.1.1.1 and February Replaced Figures 2.1.1-1, 2.1.1-2, and 2.1.1-3 to contain 2.1.1.2 2018 correct reference to water level above which Primary Frontal Dune reservoir volume is determined. Coastal Erosion February 2018 Guidance Document 40 Page ii Table of Contents 1.0 Overview ............................................................................................................................ 1 1.1 Beach and Shoreline Settings ........................................................................................ 2 1.1.1 Sandy Beach Backed by High Sand Dune: ............................................................. 3 1.1.2 Sandy Beach Backed by Low Sand Dune Berm: .................................................... 4 1.1.3 Sandy Beach Backed by Shore Protection Structure: ............................................. 4 1.1.4 Mixed Grain Size Beach .........................................................................................
    [Show full text]
  • Upward Shallowing Platform Cycles a Response to 2.2 Billion Years of Lowamplitude, Highfrequency Milankovitch Band Sea Level
    PALEOCEANOGRAPHY,VOL. 1, NO. 4, PAGES 403-416, DECEMBER 1986 UPWARD SHALLOWING PLATFORM CYCLES: A RESPONSE TO 2.2 BILLION YEARS OF LOW-AMPLITUDE, HIGH-FREQUENCY (MILANKOVITCH BAND) SEA LEVEL OSCILLATIONS J. P. Grotzinger Lamont-Doherty Geological Observatory, Palisades, New York Abstract. Shallow-water carbonate perhaps influencing global sea level platforms, characterized by sequences of through minor changes related to small- small-scale upward shallowing cycles, are scale continental or alpine glaciation. common in the Phanerozoic and Proterozoic It is possible, then, that Milankovitch stratigraphic record. Proterozoic small- band climatic forcing has occurred for at scale cycles are commonly 1 to 10 m thick, least the last 2.2 billion years of earth have asymmetrically arranged facies, and history. are strikingly similar to Phanerozoic platform cycles. In some platform INTRODUCTION sequences (eg. Rocknest, Wallace, and Helena formations of early to middle The stratigraphic record of geologic Proterozoic age), it can be demonstrated history is characterized by intervals of that the lateral distribution of facies pronounced rhythmic or cyclic arrangement within cycles relates to systematic of facies such that repetitive groups of variations in platform paleogeography and rock units have component facies which topography. In the Rocknest formation, tend to occur in certain order. cycles with intervals of tepees and Sedimentary cyclicity has been documented pisolitic breccia formed on a topographic in many paleoenvironmental settings high (shoal complex) near the shelf edge ranging from fluvial to deep sea, in both rim, and provide evidence for eustatic carbonate- and siliciclastic-dominated falls in sea level at the end of each systems [e.g.
    [Show full text]
  • A Geoarchaeological Perspective on the Challenges and Trajectories of Mississippi Delta Communities
    Geomorphology 360 (2020) 107132 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph A geoarchaeological perspective on the challenges and trajectories of Mississippi Delta communities Elizabeth L. Chamberlain a,b,c,⁎, Jayur M. Mehta d, Tony Reimann c,JakobWallingac a Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN, USA b Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA c Netherlands Centre for Luminescence Dating, Soil Geography and Landscape group, Wageningen University, Wageningen, the Netherlands d Department of Anthropology, Florida State University, Tallahassee, FL, USA article info abstract Article history: Recent geochronology of the Mississippi Delta of coastal Louisiana, USA, provides a high-resolution record of land Received 31 October 2019 growth that facilitates the study of ancient settlement patterns in relation to delta evolution. We use stratigraphy Received in revised form 27 February 2020 and optically stimulated luminescence (OSL) dating to show that two Late Holocene earthen mounds were con- Accepted 27 February 2020 structed several hundred years after the land emerged from open water. This multi-century pause allowed nat- Available online 2 March 2020 ural processes of overbank and crevasse splay deposition to elevate the land surface, reduce flood risk, and foster desirable environmental conditions prior to human occupation. These results are applied to obtain new age con- Keywords: Coupled human-natural systems straints for a large number of at-risk or lost archaeological sites with little-to-no absolute chronology. We use our Mississippi Delta findings to comment on prehistoric, contemporary, and future human-landscape interactions in the Mississippi Optically stimulated luminescence dating Delta and other deltaic environments.
    [Show full text]